U.S. patent number 11,069,738 [Application Number 16/384,014] was granted by the patent office on 2021-07-20 for infrared detector and infrared sensor including the same.
This patent grant is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The grantee listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Sanghun Lee, Changyoung Park.
United States Patent |
11,069,738 |
Park , et al. |
July 20, 2021 |
Infrared detector and infrared sensor including the same
Abstract
An infrared detector and an infrared sensor including the
infrared detector are provided. The infrared detector includes a
plurality of quantum dots spaced apart from each other and
including a first component, a first semiconductor layer covering
the plurality of quantum dots, and a second semiconductor layer
covering the first semiconductor layer.
Inventors: |
Park; Changyoung (Yongin-si,
KR), Lee; Sanghun (Seoul, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-si |
N/A |
KR |
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Assignee: |
SAMSUNG ELECTRONICS CO., LTD.
(Suwon-si, KR)
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Family
ID: |
1000005685896 |
Appl.
No.: |
16/384,014 |
Filed: |
April 15, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190245001 A1 |
Aug 8, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15870022 |
Jan 12, 2018 |
10304896 |
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Foreign Application Priority Data
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Aug 28, 2017 [KR] |
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10-2017-0108847 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
31/03845 (20130101); H01L 27/14694 (20130101); G01J
5/0853 (20130101); A61B 5/443 (20130101); G01J
1/44 (20130101); H01L 31/1013 (20130101); H01L
31/105 (20130101); H01L 31/035236 (20130101); G01N
21/3554 (20130101); B82Y 20/00 (20130101); G01J
5/024 (20130101); H01L 27/14669 (20130101); H01L
31/03046 (20130101); H01L 31/109 (20130101); H01L
27/146 (20130101); H01L 31/022466 (20130101); H01L
31/035218 (20130101); G01J 5/046 (20130101); H01L
27/14649 (20130101); G01J 2001/4446 (20130101) |
Current International
Class: |
H01L
21/00 (20060101); H01L 31/0304 (20060101); G01J
5/04 (20060101); B82Y 20/00 (20110101); G01J
5/02 (20060101); H01L 31/0384 (20060101); H01L
31/101 (20060101); H01L 31/105 (20060101); G01J
5/08 (20060101); H01L 27/146 (20060101); H01L
31/0352 (20060101); H01L 31/0224 (20060101); H01L
31/109 (20060101); A61B 5/00 (20060101); G01N
21/3554 (20140101); G01J 1/44 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2002-90298 |
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Mar 2002 |
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JP |
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2010-103202 |
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May 2010 |
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JP |
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2011-171672 |
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Sep 2011 |
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JP |
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2016-535428 |
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Nov 2016 |
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JP |
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WO-2006006469 |
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Jan 2006 |
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WO |
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Other References
Communication dated Sep. 26, 2018, issued by the European Patent
Office in counterpart European Application No. 18158666.0. cited by
applicant .
European Search Report dated Jan. 14, 2019 issued in Application
No. 18158666.0-1020. cited by applicant .
Hsu, Wei-Cheng, et al, "Wavelength tuning of surface plasmon
coupled quantum well infrared photodetectors", vol. 26, No. 1, Jan.
8, 2018, Optics Express, pp. 552-558. cited by applicant.
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Primary Examiner: Menz; Laura M
Attorney, Agent or Firm: Sughrue Mion, PLLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation application of U.S. patent application Ser.
No. 15/870,022, filed Jan. 12, 2018, in the U.S. Patent and
Trademark Office, which claims priority from Korean Patent
Application No. 10-2017-0108847, filed on Aug. 28, 2017, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
Claims
What is claimed is:
1. An infrared detector comprising: a substrate; a first electrode,
disposed on the substrate; and an infrared-absorbing layer disposed
on the first electrode, comprising a plurality of quantum dots
configured to absorb infrared light having a width of wavelength
band of about 50 nm or less within which a responsivity of the
infrared light absorbed by the plurality of quantum dots is about
0.4 or more and generate a current corresponding to absorbed
infrared light; and a second electrode disposed on the
infrared-absorbing layer, wherein the first electrode, the
infrared-absorbing layer, and the second electrode are sequentially
arranged from the substrate, and the current generated in the
infrared-absorbing flows in a direction perpendicular to the
substrate.
2. The infrared detector of claim 1, wherein the infrared light
comprises a wavelength band absorbed by moisture.
3. The infrared detector of claim 1, wherein the infrared light is
received from a target object and the infrared-absorbing layer
generates a current having a magnitude in inverse proportion to a
content of moisture in the target object.
4. The infrared detector of claim 1, wherein a center wavelength is
about 1450 nm.
5. The infrared detector of claim 1, wherein the infrared-absorbing
layer comprises a first infrared-absorbing layer and a second
infrared-absorbing layer arranged in a direction from the first
electrode to the second electrode.
6. The infrared detector of claim 1, wherein one of the first
electrode and the second electrode comprises a semiconductor layer
doped with n-type impurities and another one of the first electrode
and the second electrode comprises a semiconductor layer doped with
p-type impurities.
7. The infrared detector of claim 1, wherein the infrared-absorbing
layer comprises at least one of a first semiconductor layer
comprising a first component and a second semiconductor layer
comprising the first component and a second component, different
from the first component.
8. The infrared detector of claim 7, wherein the plurality of
quantum dots comprising the second component.
9. The infrared detector of claim 7, wherein the second
semiconductor layer covers the plurality of quantum dots.
10. The infrared detector of claim 7, wherein a wavelength band of
the absorbed infrared light is determined by a content of the
second component in the infrared-absorbing layer.
11. The infrared detector of claim 7, wherein the second component
comprises In.
12. The infrared detector of claim 7, wherein an energy band of the
second semiconductor layer is between an energy band of the
plurality of quantum dots and an energy band of the first
semiconductor layer.
13. The infrared detector of claim 7, wherein an energy band of the
plurality of quantum dots is lower than an energy band of the first
semiconductor layer and lower than an energy band of the second
semiconductor layer.
14. The infrared detector of claim 7, wherein the substrate
comprises the first a component.
15. The infrared detector of claim 7, wherein at least one of the
first component and the second component is a Group III
element.
16. The infrared detector of claim 7, wherein the first
semiconductor layer comprises a first compound comprising the first
component and a third component, different from the first component
and the second component, and the second semiconductor layer
comprises a second compound comprising the first component, the
second component, and the third component.
17. An infrared sensor comprising a plurality of infrared
detectors, each identical to the infrared detector according to
claim 1, wherein the infrared sensor is configured to detect the
infrared light received from a target object.
18. The infrared sensor of claim 17, wherein the plurality of
infrared detectors comprise a first infrared detector and a second
infrared detector, arranged in a direction perpendicular to a
direction of incidence of the infrared light on the infrared
sensor.
19. The infrared sensor of claim 17, wherein the plurality of
infrared detectors comprise a third infrared detector and a fourth
infrared detector, arranged in a direction of incidence of the
infrared light on the infrared sensor.
20. An infrared detector comprising: a substrate; a first
electrode, disposed on the substrate; and an infrared-absorbing
layer disposed on the first electrode, comprising a plurality of
quantum dots configured to absorb infrared light having a width of
wavelength band of about 50 nm or less within which a responsivity
of the infrared light absorbed by the plurality of quantum dots is
about 0.4 or more and generate a current corresponding to absorbed
infrared light; and a second electrode disposed on the
infrared-absorbing layer, wherein one of the first electrode and
the second electrode comprises a semiconductor layer doped with
n-type impurities and another one of the first electrode and the
second electrode comprises a semiconductor layer doped with p-type
impurities.
Description
BACKGROUND
1. Field
Apparatuses consistent with exemplary embodiments relate to
infrared detectors, and more particularly, to infrared detectors
capable of absorbing infrared light and infrared sensors including
the infrared detectors.
2. Description of the Related Art
Infrared images may be generated by detecting infrared light
emitted from objects by using infrared detectors. Infrared images
are typically generated by light in wavelength regions that are not
identifiable by the naked human eye. However, infrared cameras
perform pixel detection using infrared detectors and perform analog
and digital signal processing to generate images that can be seen
by the human eye. These infrared images are used in various fields
such as the defense industry, medical equipment, surveillance, and
security.
Infrared light is harmless to the human body and thus may be used
for measuring biometric information of the human body, for example,
a content of moisture and the like. However, since specific
substances in the human body react only to specific frequencies of
infrared light, an infrared detector uses a band pass filter to
obtain information about the substance. Thus, with the inclusion of
a band pass filter, it is difficult to miniaturize an infrared
detector.
SUMMARY
One or more exemplary embodiments may provide infrared detectors
and infrared sensors which absorb only infrared light in a specific
wavelength band.
One or more exemplary embodiments may provide are infrared
detectors and infrared sensors which are not sensitive to
temperature.
Additional exemplary aspects and advantages will be set forth in
part in the description which follows and, in part, will be
apparent from the description, or may be learned by practice of the
presented exemplary embodiments.
According to an aspect of an exemplary embodiment, an infrared
detector includes: a substrate; a first electrode, disposed on the
substrate; and an infrared-absorbing layer disposed on the first
electrode, wherein the infrared-absorbing layer absorbs incident
infrared light in a specific wavelength band and generates a
current corresponding to absorbed infrared light; and, a second
electrode disposed on the infrared-absorbing layer, wherein the at
least one infrared-absorbing layer includes: a first semiconductor
layer including a first component; a plurality of quantum dots,
spaced apart from each other on the first semiconductor layer and
including a second component different from the first component;
and a second semiconductor layer including the first component and
the second component and covering the plurality of quantum
dots.
The specific wavelength band may be determined by a content of the
second component in the at least one infrared-absorbing layer.
A center wavelength of the specific wavelength band may be
proportional to a content of the second component.
A center wavelength of the specific wavelength band may be 1 to 3
.mu.m.
An energy band of the second semiconductor layer may be between an
energy band of the quantum dots and an energy band of the first
semiconductor layer.
The quantum dots may have a lower energy band than the first
semiconductor layer and the second semiconductor layer.
The substrate may include the first component.
At least one of the first component and the second component may be
a Group III element.
The first semiconductor layer may include a compound comprising the
first component and a third component different from the first
component and the second component, and the second semiconductor
layer may include a compound comprising the first component, the
second component, and the third component.
The third component may be a Group V element.
The at least one infrared-absorbing layer may include first and
second infrared-absorbing layers arranged in a direction from the
first electrode to the second electrode.
The infrared detector may further include at least one of: a first
cladding layer between the first electrode and the
infrared-absorbing layer and having an energy band higher than an
energy band of the infrared-absorbing layer; and a second cladding
layer between the second electrode and the infrared-absorbing layer
and having an energy band higher than the energy band of the
infrared-absorbing layer.
At least one of the first and second cladding layers may include a
fourth component that is different from the first and second
components.
The fourth component may be a metal.
The infrared detector may further include a third semiconductor
layer between the at least one infrared-absorbing layer and the
second electrode.
The third semiconductor layer may include a same material as the
first semiconductor layer.
A sum of thicknesses of the at least one infrared-absorbing layer
and the third semiconductor layer may be equal to or greater than a
wavelength of the infrared light.
The sum of the thicknesses of the at least one infrared-absorbing
layer and the third semiconductor layer may be a multiple of the
wavelength of the infrared light.
One of the first electrode and the second electrode may include a
semiconductor layer doped with n-type impurities and the other may
include a semiconductor layer doped with p-type impurities.
The second electrode may include a transparent electrode.
The second electrode may overlap a portion of the
infrared-absorbing layer, as viewed from an incident direction of
the infrared light on the infrared detector.
According to an aspect of another exemplary embodiment, an infrared
sensor includes a plurality of infrared detectors identical to the
infrared detector and detecting infrared light reflected from a
target object.
The plurality of infrared detectors may include a first infrared
detector and a second infrared detector, arranged in a direction
perpendicular to an incident direction of light.
The first infrared detector and the second infrared detector may
absorb light of a same wavelength.
A substrate of the first infrared detector and a substrate of the
second infrared detector may together comprise a single layer
common to the first infrared detector and the second infrared
detector.
A first electrode of the first infrared detector and a second
electrode of the second infrared detector may be connected to each
other by an electrode pad.
The plurality of infrared detectors may include a third infrared
detector and a fourth infrared detector, arranged in a direction
parallel to an incident direction of light.
The third infrared detector and the fourth infrared detector may
absorb light having different wavelengths.
BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other exemplary aspects and advantages will become
apparent and more readily appreciated from the following
description of the exemplary embodiments, taken in conjunction with
the accompanying drawings in which:
FIG. 1 is a cross-sectional view schematically illustrating an
infrared detector according to an exemplary embodiment;
FIG. 2 is a graph showing threshold currents of various crystal
structures according to temperature;
FIG. 3A is a graph showing a wavelength band within which infrared
light is absorbed by a bulk structure;
FIG. 3B is a graph showing a wavelength band within which infrared
light is absorbed by quantum dots;
FIG. 4 is a graph showing the wavelength of infrared light absorbed
by quantum dots according to an exemplary embodiment and the
wavelength of infrared light absorbed by quantum dots doped with
the material of a first semiconductor layer;
FIG. 5 is a table showing a relationship between a center
wavelength and the content of indium (In), according to an
exemplary embodiment;
FIG. 6 is a diagram illustrating an energy band of an
infrared-absorbing layer in an infrared detector according to an
exemplary embodiment;
FIG. 7 is a cross-sectional view illustrating an infrared detector
according to another exemplary embodiment;
FIG. 8 is a diagram illustrating energy bands of an
infrared-absorbing layer and cladding layers of FIG. 7;
FIG. 9 is a view illustrating an infrared sensor according to an
exemplary embodiment;
FIG. 10 is a view illustrating an infrared sensor according to
another exemplary embodiment;
FIG. 11 is a graph showing light absorption rates according to
materials;
FIG. 12A shows a result obtained by photographing a plurality of
sheets having different moisture content ratios with a general
camera; and
FIG. 12B shows a result obtained by photographing a plurality of
sheets having different moisture content ratios with an infrared
sensor.
DETAILED DESCRIPTION
Infrared detectors and infrared sensors including infrared
detectors will now be described in detail with reference to the
accompanying drawings. In the drawings, like reference numerals
refer to like elements throughout and the sizes of elements are
exaggerated for clarity and convenience of explanation.
It will be understood that when an element or layer is referred to
as being "on," another element or layer may include an element or a
layer that is directly and indirectly on/below and left/right sides
of the other element or layer. Hereafter, the inventive concept
will be described more fully with reference to the accompanying
drawings, in which exemplary embodiments of the inventive concept
are shown.
It will be understood that, although the terms "first," "second,"
etc. may be used herein to describe various elements, the elements
should not be limited by these terms. These terms are only used to
distinguish one element from another element. Expressions such as
"at least one of," when preceding a list of elements, modify the
entire list of elements and do not modify the individual elements
of the list.
FIG. 1 is a cross-sectional view schematically illustrating an
infrared detector 100 according to an exemplary embodiment. The
infrared detector 100 according to the exemplary embodiment may
detect near infrared light, e.g., infrared light having a
wavelength between about 750 nm and 3000 nm. As shown in FIG. 1,
the infrared detector 100 may include a substrate 10, first and
second electrodes 20 and 30 that are disposed on the substrate 10
and spaced apart from one another, and one or more
infrared-absorbing layers 40 disposed between the first and second
electrodes 20 and 30 and which absorb infrared light in a specific
wavelength band to generate a current.
The infrared detector 100 may include a Group III-V semiconductor
material. By forming layers of the infrared detector 100 with
materials having similar lattice constants, it is easily possible
to stack the layers and miniaturize the infrared detector 100.
The substrate 10 may include a Group III-V semiconductor material,
and may include the same material as some layers of the
infrared-absorbing layer 40 described below. For example, the
substrate 10 may include GaAs.
The first and second electrodes 20 and 30 may include a conductive
material, e.g., a metal material or a conductive oxide.
Specifically, the first and second electrodes 20 and 30 may include
a transparent conductive material. For example, the first and
second electrodes 20 and 30 may include a metal oxide such as
indium tin oxide (ITO) or indium zinc oxide (IZO), a metal
nanoparticle dispersion thin film such as Au or Ag, a carbon
nanostructure such as carbon nanotubes (CNTs) or graphene, or a
conductive polymer such as poly(3,4-ethylenedioxythiophene)
(PEDOT), polypyrrole (PPy), or poly(3-hexylthiophene) (P3HT).
Alternatively, the first and second electrodes 20 and 30 may
include an impurity-doped semiconductor material. The first
electrode 20 may be a semiconductor layer doped with impurities of
a first type and may include a Group III-V semiconductor material.
For example, the first electrode 20 may include GaAs doped with
n-type impurities such as Si, Ge, Se, or Te. The second electrode
30 may be a semiconductor layer doped with impurities of a second
type and may include a Group III-V semiconductor material. For
example, the second electrode 30 may include GaAs doped with p-type
impurities. As the p-type impurities, Mg, Zn, Be or the like may be
used.
The infrared-absorbing layer 40 may absorb incident infrared light
only within a specific wavelength band. When infrared light is
incident on the infrared-absorbing layer 40, electrons, that have
absorbed the energy of an energy band gap corresponding to the
infrared light, move, resulting in an imbalance of electrons and
holes, and a current is generated in accordance with the imbalance
of electrons and holes. The current may flow from the first
electrode 20 to the second electrode 30 or from the second
electrode 30 to the first electrode 20 through the
infrared-absorbing layer 40.
The infrared-absorbing layer 40 may also include a Group III-V
semiconductor material. The infrared-absorbing layer 40 may include
a first semiconductor layer 42, a plurality of quantum dots 44 that
are spaced apart from each other on the first semiconductor layer
42, and a second semiconductor layer 46 covering the plurality of
quantum dots 44.
The first semiconductor layer 42 may include a first component
including a Group III element. For example, the first semiconductor
layer 42 may include a Group III-V semiconductor material. The
first semiconductor layer 42 may include a material having the
highest energy band of the infrared-absorbing layer 40. For
example, the first semiconductor layer 42 may include GaAs. The
first semiconductor layer 42 may determine a wavelength band within
which infrared light is absorbed by the infrared-absorbing layer
40.
The plurality of quantum dots 44 may be arranged on the first
semiconductor layer 42. Each of the plurality of quantum dots 44
may directly contact the first semiconductor layer 42. The
plurality of quantum dots 44 may be randomly arranged.
The quantum dots 44 may be nanocrystals of a semiconductor material
having a diameter of about 10 nm or less. As a method of forming
nanocrystals as the quantum dots 44, a vapor deposition method such
as metal organic chemical vapor deposition (MOCVD) or molecular
beam epitaxy (MBE), a chemical wet method in which a precursor
material is added to an organic solvent to grow crystals, or the
like may be used.
The quantum dots 44 may include a second component including a
Group III element. For example, the quantum dots 44 may be
nanocrystals of a Group III-V compound semiconductor. The Group
III-V compound semiconductor nanocrystal may be any one selected
from the group consisting of GaN, GaP, GaAs, AN, AlP, AlAs, InN,
InP, InAs, GaNP, GaNAs, GaPAs, AlNP, AlNAs, AlPAs, InNP, InNAs,
InPAs, GaAlNP, GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs, InAlNP,
InAlNAs, and InAlPAs. When the first semiconductor layer 42
includes a GaAs material, the quantum dots 44 may include InAs
having a similar lattice constant.
The nanosize quantum dots 44 exhibit a quantum confinement effect,
such that a bandgap becomes larger and the bandgap has a
discontinuous bandgap structure like one individual atom, unlike a
bulk structure.
The quantum dots 44 are not limited to a specific structure but may
have a single structure including only a core or may have any one
selected from a core-single shell structure including a shell
having a core and a single layer and a core-multiple shell
structure including a shell having a core and multiple layers.
The reason why the quantum dots 44 are included in the
infrared-absorbing layer 40 is that the quantum dots 44 exhibit a
small change in a threshold current according to temperature. FIG.
2 is a graph showing threshold currents of various crystal
structures according to temperature. As shown in FIG. 2, a bulk
structure has a large change in a threshold current according to
temperature. Thus, when applying a bulk structure to an infrared
detector, it is necessary to keep the temperature of the infrared
detector constant to improve the accuracy of the infrared detector.
That is, the infrared detector may require a cooler to maintain a
constant temperature. However, the quantum dots 44 do not require a
cooler because the threshold current of the quantum dots 44 is
almost constant according to temperature.
In addition, the quantum dots 44 may serve as seeds in depositing
materials having different lattice constants to facilitate
formation of layers including the materials. For example, when a
layer including InGaAs, having a lattice constant different from
that of GaAs, is formed on a layer including GaAs, the quantum dots
44 may serve as an adhesive.
In addition, the quantum dots 44 may be sensitive to light in a
specific wavelength band. FIG. 3A is a graph showing a wavelength
band within which infrared light is absorbed by a bulk structure,
and FIG. 3B is a graph showing a wavelength band within which
infrared light is absorbed by quantum dots. The bulk structure used
to obtain the graph of FIG. 3A includes InGaAs, and the quantum
dots used to obtain the graph of FIG. 3B include InAs. As shown in
FIG. 3A, the bulk structure absorbs infrared light in a wide
wavelength band. The width of a wavelength band within which the
responsivity of the infrared light absorbed by the bulk structure
is about 0.4 or more is about 750 nm. On the other hand, as shown
in FIG. 3B, the quantum dots absorb infrared light within a narrow
wavelength band. The width of the wavelength band within which the
responsivity of the infrared ray absorbed by the quantum dots is
about 0.4 or more is about 50 nm.
An infrared detector including a bulk structure includes a bandpass
filter as a component to determine whether the infrared detector
absorbs infrared light in a particular wavelength band. However, an
infrared detector including quantum dots has a narrow wavelength
band within which infrared light is detected, and thus need not
include a separate band filter. Thus, the structure of the infrared
detector including the quantum dots may be simplified.
The infrared-absorbing layer 40 may include the second
semiconductor layer 46 covering the plurality of quantum dots 44.
The second semiconductor layer 46 may include a material having an
energy band that is greater than that of the quantum dots 44. The
energy band of the second semiconductor layer 46 may be greater
than the energy band of the quantum dots 44 and may be less than
the energy band of the first semiconductor layer 42. The second
semiconductor layer 46 may include a second component contained in
the quantum dots 44 and a second component including a Group III
element, which is different from the second component contained in
the quantum dots 44. For example, when the quantum dots 44 include
InAs, the second semiconductor layer 46 may include InGaAs.
The first semiconductor layer 42, the plurality of quantum dots 44,
and the second semiconductor layer 46 may include the same
component. Each of the first semiconductor layer 42, the plurality
of quantum dots 44, and the second semiconductor layer 46 may
include a third component including a Group V element. For example,
the first semiconductor layer 42 may include GaAs, the quantum dots
44 may include InAs, and the second semiconductor layer 46 may
include InGaAs. By including the same material as described above,
stacking between layers is facilitated.
The infrared detector 100 may further include a third semiconductor
layer 50 between the infrared-absorbing layer 40 and the second
electrode 30. The third semiconductor layer 50 may include the same
material as the first semiconductor layer 42. For example, the
third semiconductor layer 50 may also include GaAs.
The upper surface of the infrared-absorbing layer 40 may be
planarized so that a plurality of infrared-absorbing layers may be
stacked. The quantum dots 44 have a crystal structure, and the
second semiconductor layer 46 may have the form of a thin film and
may cover the quantum dots 44. Thus, the surface of the second
semiconductor layer 46 may be curved by the quantum dots 44, and
the infrared-absorbing layer 40 may be planarized by the stacking
of the first semiconductor layer 42.
The infrared detector 100 may include one or more
infrared-absorbing layers 40. When the infrared detector 100
includes one or more infrared-absorbing layers 40, the one or more
infrared-absorbing layers 40 may be arranged in a direction from
the first electrode 20 to the second electrode 30. For example, the
one or more infrared-absorbing layers 40 may include a first
infrared-absorbing layer 40a, disposed on and in contact with the
first electrode 20, a second infrared-absorbing layer 40b, disposed
below and in contact with the third semiconductor layer 50, and a
third infrared-absorbing layer 40c arranged between the first
infrared-absorbing layer 40a and the second infrared-absorbing
layer 40b.
The one or more infrared-absorbing layers 40 and the third
semiconductor layer 50 may determine the content of In component
contained in the infrared-absorbing layers 40. Since the In
component is contained in the quantum dots 44 and the second
semiconductor layer 46, the content of the In component may be
adjusted by adjusting the thicknesses of the first semiconductor
layer 42 and the third semiconductor layer 50. For example, since
the content of the Ga component increases as the thicknesses of the
first semiconductor layer 42 and of the third semiconductor layer
50 increase, the content of the In component may be comparatively
reduced. In the infrared detector 100 according to the present
exemplary embodiment, the content of the In component may be
determined so that infrared light having a center wavelength of
about 1 to 3 .mu.m is absorbed.
The sum (t) of the thicknesses of the one or more
infrared-absorbing layers 40 and the third semiconductor layer 50
may be greater than or equal to the wavelength of the infrared
light to be detected. For example, the sum of the thicknesses of
the one or more infrared-absorbing layers 40 and the third
semiconductor layer 50 may be a multiple of the wavelength of the
infrared light to be detected. Thus, the infrared light to be
detected may be stably incident on the infrared-absorbing layer
40.
FIG. 4 is a graph showing the wavelength of infrared light absorbed
by quantum dots according to an exemplary embodiment and the
wavelength of infrared light absorbed by quantum dots doped with a
second semiconductor layer. As shown in FIG. 4, it may be seen that
quantum dots (i.e., the quantum dots 44), including InAs, react to
infrared light having a center wavelength of about 1350 nm, whereas
quantum dots doped with InGaAs react to infrared light having a
center wavelength of about 1460 nm. That is, it may be seen that
the degree of doping of InGaAs may change the wavelength band of
infrared light to which quantum dots react.
Also, it may be seen from FIG. 4 that even if the wavelength band
of infrared light to which quantum dots react is changed, the width
of the wavelength band of the infrared light to which quantum dots
react is almost constant. For example, quantum dots including InAs
and a responsivity of quantum dots doped with InGaAs may be 0.4 or
more at the width of the wavelength band of about 50 nm. Thus, the
detection sensitivity of infrared light may be maintained while
adjusting a wavelength band to be detected by the doping of
InGaAs.
The band gap energy Eg(x) of InxGa1-xAs is expressed by Equation
(1). Eg(x)=1.425 eV-1.501x eV+0.436x.sup.2 eV [Equation 1]
Here, x is equal to or greater than 0 and is equal to or less than
10 (i.e., 0.ltoreq.x.ltoreq.10).
As shown in Equation 1, the band gap energy Eg(x) changes depending
on the content of In component. A change in the bandgap energy
Eg(x) means that the wavelength of infrared light to be absorbed
may be changed.
FIG. 5 is a table showing a relationship between a center
wavelength and the content of In component, according to an
exemplary embodiment. As shown in FIG. 5, it may be seen that the
content of In component and a band gap energy are proportional to
each other and the content of In component and the center
wavelength of infrared light to be absorbed are inversely
proportional to each other. Thus, the center wavelength of infrared
light to be absorbed may be adjusted by controlling the content of
In component.
FIG. 6 is a diagram illustrating an energy band of the
infrared-absorbing layer 40 in the infrared detector 100 according
to the exemplary embodiment. When the first semiconductor layer 42
includes GaAs, the quantum dots 44 include InAs, and the second
semiconductor layer 46 includes InGaAs, the infrared-absorbing
layer 40 may have an energy band as shown in FIG. 6. When electrons
of the infrared-absorbing layer 40 absorb infrared light having a
specific wavelength, for example, the wavelength of 1450 nm, the
electrons are activated and move.
FIG. 7 is a cross-sectional view illustrating an infrared detector
100a according to another exemplary embodiment. When comparing FIG.
7 with FIG. 1, the infrared detector 100a of FIG. 7 may further
include a first cladding layer 60 arranged between a first
electrode 20 and an infrared-absorbing layer 40 and a second
cladding layer 70 arranged between a second electrode 30 and the
infrared-absorbing layer 40. The first cladding layer 60 and the
second cladding layer 70 may include a material having an energy
band higher than the energy band of the infrared-absorbing layer
40. The first cladding layer 60 and the second cladding layer 70
may include a metal material. For example, the first cladding layer
60 and the second cladding layer 70 may include AlGaAs. Even if
electrons of the infrared-absorbing layer 40 are activated, the
first cladding layer 60 and the second cladding layer 70 may allow
only electrons having a higher energy band than the first cladding
layer 60 and the second cladding layer 70 to escape from the
infrared-absorbing layer 40, thereby increasing the electron
concentration of the infrared-absorbing layer 40. The infrared
detector 100a may include both the first cladding layer 60 and the
second cladding layer 70 or may include only one of the first
cladding layer 60 and the second cladding layer 70.
FIG. 8 is a diagram illustrating energy bands of the
infrared-absorbing layer 40 and the first and second cladding
layers 60 and 70 of FIG. 7. When the first and second cladding
layers 60 and 70 include AlGaAs, the quantum dots 44 include InAs,
and the second semiconductor layer 46 includes InGaAs, the
infrared-absorbing layer 40 and the first and second cladding
layers 60 and 70 may have energy bands as shown in FIG. 8. Since a
band gap up to a first energy band is 0.855 eV, electrons may be
activated when infrared light of about 1450 nm is incident on the
infrared-absorbing layer 40. However, only electrons having a
higher energy band than the first and second cladding layers 60 and
70 may escape from the infrared-absorbing layer 40 and flow to the
first electrode 20 or the second electrode 30.
An infrared sensor may be formed by arranging a plurality of
infrared detectors, for example, the infrared detectors 100 or 100a
described above. The plurality of infrared detectors of the
infrared sensor may detect infrared light of the same wavelength
band or detect infrared light of different wavelength bands. The
wavelength band of infrared light to be detected may vary depending
on the content of In in the an infrared-absorbing layer included in
each of the infrared detectors 100 or 100a.
FIG. 9 is a view illustrating an infrared sensor 200 according to
an exemplary embodiment. As shown in FIG. 9, the infrared sensor
200 may include a plurality of infrared detectors, for example,
first and second infrared detectors 210 and 220. For example, the
first and second infrared detectors 210 and 220 may be stacked in a
direction parallel to an incident direction of infrared light. Each
of the first and second infrared detectors 210 and 220 may
correspond to the infrared detector 100 shown in FIG. 1 or the
infrared detector 100a shown in FIG. 8.
A second electrode 213 of the first infrared detector 210 and a
first electrode 222 of the second infrared detector 220 may be
connected to each other by an electrode contact 230. The second
electrode 213 of the first infrared detector 210 and the first
electrode 222 of the second infrared detector 220 may be a single
electrode common to both the first infrared detector 210 and the
second infrared detector 220. The second electrode 213 of the first
infrared detector 210, the first electrode 222 of the second
infrared detector 220, and a second electrode 223 of the second
infrared detector 220 may be transparent electrodes in order to
increase an incident amount of infrared light.
The content of In may be different between an infrared-absorbing
layer 214 of the first infrared detector 210 and an
infrared-absorbing layer 224 of the second infrared detector 220.
Thus, the first infrared detector 210 and the second infrared
detector 220 may detect different wavelength bands. The longer the
wavelength, the higher the transmittance, and thus, the first
infrared detector 210 may be designed to detect a longer wavelength
than the second infrared detector 220. For example, the content of
In may be adjusted so that the first infrared detector 210 detects
infrared light having a center wavelength of about 1650 nm and the
second infrared detector 220 detects infrared light having a center
wavelength of about 1450 nm.
FIG. 10 is a view illustrating an infrared sensor 300 according to
another exemplary embodiment. As shown in FIG. 10, the infrared
sensor 300 may include a plurality of pixels P arranged on a
substrate 310. The plurality of pixels P may be arranged in a
direction perpendicular to an incident direction of infrared light.
Since the plurality of pixels P are arranged in the direction
perpendicular to the incident direction of infrared light, an
object having a certain area may be photographed at once. The
pixels P may be formed by the infrared detector 100.
The substrate 310 of the infrared sensor 300 may include a Group
III-V semiconductor material. For example, the substrate 310 may
include GaAs.
A common electrode 320 may be arranged on the substrate 310. The
common electrode 320 may include a metal material or a conductive
oxide. Alternatively, the common electrode 320 may include a
semiconductor material doped with impurities. For example, the
common electrode 320 may include GaAs doped with n-type
impurities.
A first cladding layer 360 may be arranged on the common electrode
320, and the first cladding layer 360 may include a material having
an energy band higher than that of an infrared-absorbing layer 340
included in each of the pixels P. For example, the first cladding
layer 360 may include AlGaAs. An electrode pad 390 may be arranged
on a portion of the first cladding layer 360. The electrode pad 390
may be connected to the common electrode 320 through a through-hole
of the first cladding layer 360.
Each pixel P may include one or more infrared-absorbing layers 340,
a third semiconductor layer 350, a second cladding layer 370, and a
pixel electrode 330. The infrared-absorbing layers 340, the third
semiconductor layer 350, and the second cladding layer 370,
included in the pixel P, may respectively correspond to the
infrared-absorbing layer 40, the third semiconductor layer 50, and
the second cladding layer 70, shown in FIG. 7.
Specifically, each of the infrared-absorbing layers 340 may include
a Group III-V semiconductor material. Each of the
infrared-absorbing layers 340 may include a first semiconductor
layer 342, a plurality of quantum dots 344 that are spaced apart
from one another on the first semiconductor layer 342, and a second
semiconductor layer 346 covering the plurality of quantum dots
344.
The first semiconductor layer 342 may also include a Group III-V
semiconductor material. The first semiconductor layer 342 may
include a material having the highest energy band of all of the
layers in the infrared-absorbing layer 340. The first semiconductor
layer 342 may also include a first component including a Group III
element. For example, the first semiconductor layer 342 may include
GaAs.
The plurality of quantum dots 344 may be randomly arranged. The
quantum dots 344 may include a second component including a Group
III element. Specifically, the quantum dots 344 may be nanocrystals
of a Group III-V-based compound semiconductor. For example, the
quantum dots 344 may include InAs.
The second semiconductor layer 346 covering the plurality of
quantum dots 344 may include a material having an energy band
higher than that of the quantum dots 344. The second semiconductor
layer 346 may include a component including a Group III element,
which is not included in the quantum dots 344. For example, when
the quantum dots 344 include InAs, the second semiconductor layer
346 may include InGaAs.
The third semiconductor layer 350 may be arranged on the
infrared-absorbing layer 340 and may include a Group III-V
semiconductor material. For example, the third semiconductor layer
350 may include GaAs.
The second cladding layer 370 may be arranged on the third
semiconductor layer 350 and may include a material having an energy
band higher than that of the infrared-absorbing layer 340. The
second cladding layer 370 may include AlGaAs, like the first
cladding layer 360.
The pixel electrode 330 may include a conductive material and may
correspond to the second electrode 30 of the infrared detector 100
shown in FIG. 1 or of the infrared detector 100a shown in FIG. 7.
For example, the pixel electrode 330 may include a metal material
or a conductive oxide. Specifically, the pixel electrode 330 may
include a transparent conductive material. For example, the pixel
electrode 330 may include a metal oxide such as ITO or IZO, a metal
nanoparticle dispersion thin film such as Au or Ag, a carbon
nanostructure such as CNT or graphene, or a conductive polymer such
as PEDOT, PPy, or P3HT.
Alternatively, the pixel electrode 330 may include a semiconductor
material doped with impurities. For example, the pixel electrode
330 may include a semiconductor material of GaAs doped with p-type
impurities.
When the material of the pixel electrode 330 is not a transparent
material, the pixel electrode 330 may have a shape having an empty
center region, in order to increase the incident amount of infrared
light. For example, the pixel electrode 330 may have the shape of a
ring arranged only on the edges of the infrared-absorbing layer
340. Alternatively, an electrode of the pixel P may have the shape
of a mesh including a plurality of openings.
The pixel P, the first cladding layer 360, the common electrode
320, and a part of the substrate 310, shown in FIG. 10, may
correspond to the infrared detector 100a shown in FIG. 7. The
infrared sensor 300 of FIG. 10 includes the first and second
cladding layers 360 and 370, but is not limited thereto. For
example, the infrared sensor 300 may omit the first and second
cladding layers 360 and 370, or may include only one of the first
and second cladding layers 360 and 370.
The infrared sensor 300 described above may be used to measure the
content of a component contained in an object. For example, the
infrared sensor 300 may be used as a sensor for measuring moisture.
FIG. 11 is a graph showing light absorption rates according to
materials. As shown in FIG. 11, it may be seen that water absorbs
more infrared light in a wavelength band of about 1450 nm. Skin
includes various materials, but the content of water in the skin is
relatively high, and thus, as shown in FIG. 11, it may be seen that
the skin has a light absorption rate similar to the light
absorption rate of water. Particularly, it may be seen that the
skin also absorbs infrared light in a wavelength band of about 1450
nm. Thus, the moisture of the skin may be measured by using
infrared light in a wavelength band of about 1450 nm.
An infrared sensor 300 according to the present exemplary
embodiment may be designed to detect infrared light in a wavelength
band of about 1450 nm in order to measure a moisture content. The
In content of an infrared-absorbing layer in the infrared sensor
300 may be determined to detect infrared light in a wavelength band
of about 1450 nm. For example, the infrared sensor 300 may be
manufactured to have an In content of about 0.43. The infrared
sensor 300 may also be used to measure other components in addition
to moisture.
FIG. 12A shows a result obtained by photographing a plurality of
sheets having different moisture content ratios with a general
camera, and FIG. 12B shows a result obtained by photographing a
plurality of sheets having different moisture content ratios with
an infrared sensor. As shown in FIG. 12A, since the general camera
is an RGB image device, the general camera does not provide
information about the content of moisture in the sheets. On the
other hand, as shown in FIG. 12B, the infrared sensor may provide a
lower luminance image with respect to a sheet having a higher
moisture content ratio. A sheet having a higher moisture content
ratio may absorb more infrared light in a wavelength band of about
1450 nm. Thus, in this case, since the infrared sensor absorbs less
infrared light, the infrared sensor generates lower current and
provides a lower luminance image.
As described above, when quantum dots are included in an infrared
detector and an infrared sensor, the infrared detector and the
infrared sensor may detect infrared light within a narrow
bandwidth. Thus, the infrared detector and the infrared sensor do
not require a separate band-pass filter. In addition, since the
threshold current in the quantum dots does not change significantly
according to temperature, the infrared detector and the infrared
sensor do not require a cooler for maintaining a constant
temperature. Thus, a small infrared detector and a small infrared
sensor may be manufactured.
In addition, since the infrared detector having a multi-layer
structure includes quantum dots having an adhesive function,
multiple layers in the infrared detector may be easily formed and
thus the manufacture of the infrared detector is facilitated.
It should be understood that exemplary embodiments described herein
should be considered in a descriptive sense only and not for
purposes of limitation. Descriptions of features or aspects within
each embodiment should typically be considered as available for
other similar features or aspects in other embodiments.
While one or more exemplary embodiments have been described with
reference to the figures, it will be understood by those of
ordinary skill in the art that various changes in form and details
may be made therein without departing from the spirit and scope as
defined by the following claims.
* * * * *